The present invention relates to a variable or stretchable diameter tube for use in a vessel inserted for performing hemodynamic research and related operations. The invention also relates to a method for making said tube.
As is known, in a lot of surgical operations, an access to the hematic flow of the patient is achieved by puncturing an arterial vessel, typically a femoral or radial artery, while holding the vessel in a pervious condition by using a specifically designed introducing or inserter element or device.
Such an inserter element conventionally comprises a medical device adapted to be used in surgical operations, for example in a hemodynamics monitoring operation, an electrocatheter installing operation, a diagnostic test and any interventional surgical procedure in general.
In particular, said inserter is used for inserting, exchanging and monitoring other medical devices, for example catheters and electrodes, installed in a patient vessel.
Such an inserter has generally a variable length, within a length range from 15 to 40 cm.
The inserter, in particular, is characterized by its inner diameter (ID), which precisely defines the size of the device which can be introduced into a given vessel.
The inserter or introducer device is held in an installed condition through the overall surgical procedure duration, and it can be left in situ even for several days from the surgical intervention.
A prior inserter conventionally comprises an extruded tube element, which is extruded from a rigid and low friction material, such as FEP and PTFE, with a comparatively small thickness and a tapering distal part.
Some prior inserters have a stiffened or reinforced construction, that is comprise through their thickness a metal stiffening framework, to prevent the tube from undesirably bulging.
The proximal part of the inserter is usually coupled to a hemostatic valve, which comprises a plastics rigid component including an inner silicone diaphragm, designed for holding the inside of the inserter insulated from the outer environment.
Such a hemostatic valve operates to prevent blood from exiting the vessel and air from entering the latter.
Said valve consists of a pre-etched silicone septum assembly, allowing a preset device to be introduced thereinto, to be held coaxially therewith.
The second or other device, accordingly, is encompassed by a silicone material providing a tight sealing.
Generally, at a lateral position and downstream of said valve, is provided a line contacting the blood and to be used for continuously monitoring the patient blood pressure.
The above mentioned inserter or introducer device is usually located by using the so-called Seldinger's procedure.
According this installing method, the patient is punctured by a puncturing needle to penetrate a patient vessel.
Then, a guide wire having a suitable length is introduced into the needle, thereby locating said guide wire at a desired region of the vessel.
Then, the needle is withdrawn and the introducer-dilator system is caused to slide on the guide wire.
The dilator or dilatator device usually comprises a flexible hose, made of a low friction material, such as PTFE, with a tapering point designed for easily penetrating the vessel, and having a maximum outer diameter equal to the inner diameter of the introducer.
A specifically designed proximal system allows the dilator to be coupled or engaged to and disengaged from the introducer, upon withdrawing it from said introducer.
At the end of such an operation, only the introducer will be held within the patient vessel.
Accordingly, the introducer or inserter must have such a stiffness as to properly oppose the resilient strength of the vessel.
In this connection it should be pointed out that the above mentioned Seldinger's method allows the vessel to be opened by a dilating hole, and not by a cut-through arrangement.
Accordingly, such an operation exploits the deforming resilient capability of the vessel, which would be also very useful at the end of the procedure, for reclosing the vessel.
In this connection it should be apparent that an incision or cut-through would be much more difficult to be healed than a hole.
The vessel, in particular, is closed by applying a manual pressure force, or by a specifically designed closing system such as a percutaneous suturing system or collagen based system.
Sometimes, a set inserter or introducer device must be changed, by replacing it with a larger or smaller diameter inserter, for example for locating or installing ventricular aiding systems, to allow a larger diameter device to be driven through the vessel.
Up to now, such an operation involved a removal of the used inserter and a repetition of Seldinger's procedure, to just relocating the inserter.
At present, the tubes making the above mentioned medical devices have a cross-sectional fixed diameter, and are made by extruding, molding, blowing and dipping making methods.
More specifically, as an exemplary brief discussion, the above rigid tubes are made by extruding methods, the softer tubes, having elastic properties, being made by dipping methods, and the strong variable section tubes being made by extruding and blowing methods.
No polymeric material is at present known having shape memory capabilities while providing a satisfactory constructional stiffness: these properties, on the contrary, are well known in steel or nickel-titanium alloy mesh arrangements, which are of broad use in this field.